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Section 2
Operational Characteristics
This section describes the basic operational characteristics of the GPS 25LP
sensor
boards. Additional information regarding input and output specifications are contained
in Section 4.
2.1 Self Test
After input power has been applied to the GPS 25LP sensor boards and periodically
thereafter, the units will perform critical self test functions and report the results over
the output channel(s). The following tests will be performed:
1) RAM check
2) FLASH test
3) Receiver test
4) Real-time clock test
5) Oscillator check
In addition to the results of the above tests, the board set will report software version
information.
2.2 Initialization
After the initial self test is complete, the GPS 25LP will begin the process of satellite
acquisition and tracking. The acquisition process is fully automatic and, under normal
circumstances, will take approximately 45 seconds to achieve a position fix (15
seconds if ephemeris data is known). After a position fix has been calculated, valid
position, velocity and time information will be transmitted over the output channel(s).
Like all GPS receivers, the GPS 25LP utilizes initial data such as last stored position,
date and time as well as satellite orbital data to achieve maximum acquisition
performance. If significant inaccuracy exists in the initial data, or if the orbital data is
obsolete, it may take 1.5 minutes to achieve a navigation solution. The GPS 25LP
AutoLocate
TM
feature is capable of automatically determining a navigation solution
without intervention from the host system. However, acquisition performance can be
improved if the host system initializes the board set following the occurrence of one or
more of the following events:
